Time-resolved, infrared (IR) spectroscopy is an important tool in physical chemistry and condensed matter physics. It is also of use in trace gas detection and atmospheric chemistry. In particular, mid-IR vibrational resonances provide a method for probing of molecular structure that can be combined with time-resolved techniques to extract information on molecular dynamics.
Owing to interest in characterizing spectroscopic transients at multiple vibrational frequencies in femtosecond IR experiments, there has been a need for multichannel IR array detectors. However, these arrays are presently limited by their finite size (typically 32 to 128 elements in linear arrays), and by their high cost. Unlike CCD arrays, traditional IR arrays are also very sensitive to thermal blackbody radiation, making thermal isolation a prerequisite for imaging. Most mid-infrared detectors must be liquid nitrogen cooled to obtain adequate sensitivity. The use of inexpensive silicon charged-coupled-device (CCD) arrays could be advantageous, but the 1.1 micron bandgap of silicon has made CCD technology unable to directly detect mid-IR radiation.
The lack of suitable multi-channel IR detectors has caused researchers measuring transient absorption spectra in the mid IR (from 1000 to 4000 cm-1) to rely on, for example, scanning an independently tunable, narrowband, probe pulse or, alternatively, shifting a nanosecond broadband dye laser into the IR and then frequency-shifting it back into the visible for optical multichannel analyzer (OMA) detection.
However there continues to be a need for further improvements in infrared spectroscopy to more efficiently measure structures and/or dynamics of interest.